Method to enhance the performance of cooling devices utilizing modified barium titanate (bt) electrocaloric ceramic materials

ABSTRACT

A method to enhance the performances of cooling devices based on barium titanate (BT) ceramics is disclosed. Such cooling is realized by utilizing at least one BT-based ceramics which exhibit large electrocaloric effect (ECE). The method enhances the large ECE performances to cover temperature range between −30 C to 80C, by introducing an invariant critical point where paraelectric phase and at least one ferroelectric phase of BT-based ceramic refrigerant coexist.

This application claims the benefit of Chinese Application No. 201510586361.3 filed Sep. 15, 2015 the entire disclosure of which is hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present disclosure is directed to a method to enhance electrocaloric effect (ECE) performances in modified Barium Titanate (BT)-based ceramics and hence enhance the performances of the cooling devices, such as heat pumps, refrigerators and air-conditioners, based on modified BT ceramics. The present disclosure relates to fields of refrigeration and thermal management devices, especially methods to enhance refrigeration capability in modified BT-based ceramics which exhibit large ECE.

BACKGROUND

In a dielectric material, its dipolar orientation can be changed by applying electric fields upon the material, causing an adiabatic temperature change or an isothermal entropy change. Such effect is known as electrocaloric effect (ECE). Upon applying an electric field, the dipoles in the dielectric material orient with respect to the electric field, reducing its dipolar entropy, raising its temperature adiabatically or ejecting heat isothermally. When the electric field is removed, dipoles return to its random orientation state, increasing its dipolar entropy, reducing its temperature adiabatically or absorbing heat isothermally. Above describes the principle of refrigeration from electrocaloric effect.

SUMMARY OF THE DISCLOSURE

This disclosure relates to cooling devices with enhanced performance which can be achieved by a method that enhances the performances of the cooling devices based on modified BT ceramics. The disclosed method enhances the ECE performances of BT-based ceramics and hence enhances the performance of cooling devices or refrigerators which are based on at least one of the said ceramics as refrigerant. With the disclosed method, BT-based ceramics would exhibit larger ECE which covers temperature range from −30-80° C.

To achieve the performance enhancement of cooling devices, the present disclosure provides a method to enhance ECE performances of BT-based ceramics. Said cooling devices is based on at least one BT-based ceramic exhibiting large ECE. Said large ECE correspond to an induced temperature change ΔT≧3° C., under an electric field E≦15 MV/m. Said large ECE occurs over a wide range of temperature from −30 to 80° C.

-   Said BT-based electrocaloric ceramic have compositions of     (Ba_(1-n)Sr_(n))(Ti_(1-x-y)Zr_(x)Sn_(y))O₃ as base ceramics or doped     (Ba_(1-n)Sr_(n))(Ti_(1-x-y)Zr_(x)Sn_(y))O₃ ceramics. Wherein 0≦n≦1,     0≦x≦1 and 0≦y≦1. Wherein A-site doping element(s) are chosen from     Li, Na, K from IA group, Ca from IIA group, Ph from IVA group, Bi     from VA group, Y from IIIB group, La, Ce, Pr, Nd, Pm, Sm from     Lanthanide series of elements, and the combinations of thereof; -   wherein B-site doping element(s) are chosen from Mg from IIA group,     In from IIIA group, Sb from VA group, Cu from IB group, Zn, Cd from     IIB group, Sc from IIIB group, Hf from IVB group, V, Nb, Ta from VB     group, Cr, W from VIB group, Mn from VIIB group, Fe, Co, Ni, Pd from     VIII group, and Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu from Lanthanide     series of elements, and combinations of thereof. -   Preferably, 0≦n≦0.5, 0.1≦x≦0.3 and 0.05≦y≦0.2.

Preferably, the doping element can be chosen from ions that have same valence state as that of replaced base ion; it can also be chosen from ions that have different valence state as that of replaced base ion.

-   Preferably, molar percentages of doping element or elements is from     0-20% of base ceramics. -   Preferably, in one embodiment of fabrication method of said     electrocaloric ceramic, it comprises procedures as, -   (1) Based on chemical formula of base ceramic     (Ba_(1-n)Sr_(n))(Ti_(1-x-y)Zr_(x)Sn_(y))O₃ and doping element types     and quantities, weigh corresponding materials and mix them to form     powder. (2) Add solvent into the mixture of powder and ball mill the     mixture. Bake to remove the solvent after ball mill and then get     ball-milled powder. (3) Pre-sinter the said ball-milled powder to     get precursor powder. (4) Add additives, sintering aids and glass     phase additives to the precursor powder and then add solvent.     Perform ball mill to the mixture, Bake to remove solvent to get raw     BT-based electrocaloric ceramic powder. (5) Press said raw BT-based     electrocaloric ceramic powder to form a raw solid shape from     BT-based electrocaloric ceramic powder. (6) Sinter said pressed     BT-based electrocaloric ceramic to get bulk BT-based electrocaloric     ceramic.

Further, in procedure (4) of above method, wherein the additives can be chosen from one or more than one from MnO2, MgO, CuO, ZnO, Sb₂O₅; the sintering aids can be chosen from one or more than one from B₂O₃, Li₂O, SiO₂, Bi₂O₃, PbO; glass phase filler can be chosen from one or more than one from B₂O₃, Li₂O, Na₂O, MgO, Al₂O₃, SiO₂, CaO, V₂O₅, Cr₂O₃, Co₂O₃, ZnO, CuO, Sb₂O₅, BaO, Bi₂O₃.

The advantage of this invention disclosure lies in the enhancement of electrocaloric effect in BT-based ceramics to improve the performances of heat-pumps or refrigerators or cooling devices that are using BT-based electrocaloric ceramics as at least one of the refrigerant. To achieve such enhancement, this invention discloses a method to form invariant critical point at which paraelectric phase is merged with at least one of the ferroelectric phases by doping BT-based ceramics to improve their electrocaloric performances. Thus modified BT-based ceramics exhibit enhanced electrocaloric performance over a temperature range from −30 to 80° C., where the invariant critical point can be adjusted to.

Barium Titanate (BaTiO₃) is a ferroelectric material with perovskite ABO₃ structure. Wherein both A-site ions and B-site ions can be substituted, by doping other element, to modify the material properties, which include various physical and chemical functional properties. Near paraelectric and ferroelectric transition temperature, the electric polarization of the material goes through abrupt change, which enables the material to have larger electrocaloric effect at nearby temperature range than that at other temperatures. By doping different elements to BaTiO₃ ceramics, we substitute ions in A-site and B-site and hence modify the electrocaloric effect of the modified material to have better performances at a temperature range of −30-80° C., Thus the performances of the cooling devices which are based on one or more BT-based cooling agent/refrigerant would have better cooling performance at the temperature range of −30-80° C.

The disclosed BT-based electrocaloric ceramics are modified by ion substitution of either or both A-site and B-site where doping ions were added by composite-doping method, donor/acceptor doping method, precursor doping methods and etc. The phase diagram of BT-based ceramics can be adjusted by doping A-site and/or B-site ions with both donor and acceptor ion, thus optimize stability of coexistence of multi-phases in the BT-based ceramics and thus improve the electrocaloric effect in the material.

The BT-based ceramics made from the method in present invention disclosure exhibit larger electrocaloric effect in a temperature range of −30-80° C. than that at other temperature ranges. In −30-80° C., electrocaloric induced temperature change ΔT≧3K under an electric field E≦15 MV/m.

BRIEF DESCRIPTION OF THE DRAWINGS

Reference is made to the attached drawings, wherein elements having the same reference numeral designations represent similar elements throughout. Understanding that these drawings describe only several embodiments of the disclosure and are, therefore, not to be considered limiting of its scope and wherein:

FIG. 1. The electric field induced temperature change as a function of electric field for Ba(Ti_(0.8)Zr_(0.2))O₃.

FIG. 2 show the temperature change for the doped material, 0.8[Ba(Ti_(0.82)Zr_(0.18))O₃]−0.2[Ba(Ti_(0.9)Sn_(0.1))O₃]. It is clear that Sn-doped BZT showed much better EC response compared with pure BZT.

DETAILED DESCRIPTION OF THE DISCLOSURE

The present disclosure provides a method to enhance the performances of a heat-pump/refrigerator that is operating a BT-based ceramics exhibiting large electrocaloric effect as at least one of the cooling agent (refrigerant). Said large electrocaloric effect is referring to at an interested temperature range, where most of cooling devices are working at, the electrcaloric effect induced temperature change is larger than that at other temperature ranges. To be specific, said electrocaloric effect induced temperature change ΔT≧3K under an electric field E≦15 MV/m in a temperature range of −30-80° C.

Wherein BT-based electrocaloric ceramic have compositions of (Ba_(1-n)Sr_(n))(Ti_(1-x-y)Zr_(x)Sn_(y))O₃ as base ceramics or a complex ceramic comprising (Ba_(1-n)Sr_(n))(Ti_(1-x-y)Zr_(x)Sn_(y))O₃ as base ceramics and other elements as dopant doped into the base ceramic. Wherein 0≦n≦1, 0≦x≦1 and 0≦y≦1. In addition, 0≦n≦0.5, 0≦x≦0.5 and 0≦y≦0.5. Preferably, 0.1≦n≦0.4, 0.1≦0.1x≦0.3 and 0.05≦y≦0.2.

Wherein A-site doping element or doping element composition can be chosen from one or a combination from Li, Na, K from IA group, Ca from IIA group, Pb from IVA group, Bi from VA group, Y from IIIB group, La, Pr, Nd, Pm, Sm from Lanthanide series of elements; wherein B-site doping element(s) can be chosen from one or a combination from Mg from IIA group, In from IIIA group, Sb from VA group, Cu from IB group, Zn, Cd from IIB group, Sc from IIIB group, Hf from IVB group, V, Nb, Ta from VB group, Cr, W from VIB group, Mn from VIIB group, Fe, Co, Ni, Pd from VIII group, and Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu from Lanthanide series of elements. For instance, the composition of base ceramics is (Ba_(1-n)Sr_(n))(Ti_(1-x-y)Zr_(x)Sn_(y))O₃, with A-site doping element of Ce, Bi, B and B-site doping element Mn and Co.

Said doping element can be chosen from ions which have same equivalent valance state of ions in base ceramics, such as Ca²⁺, Mn⁴⁺, Ce⁴⁺, Hf⁴⁺. Pb²⁺; they can also be chosen from element ions that has different valance state of ions on base ceramics, such as Co³⁺, Nb⁵⁺, Sb⁵⁺, La³⁺ and W⁶⁺.

In addition, said doping elements composition can be an ion composition that has same valance state in total as that of ion in base ceramics, such as, Na_(1/2) ⁺, Mn_(1-m) ⁴⁺Ce_(m) ⁴⁺ (0≦m≦1), Mg_(1/3) ²⁺Nb_(2/3) ⁵⁺, Fe_(1/2) ³⁺Nb_(1/2) ⁵⁺; they can also be chosen from an ion composition that has different equivalent valance state in total from that of ions in base ceramics, such as Co_(1/2) ³⁺Hf_(1/2) ⁴⁺, La_(1/2) ³⁺W_(1/2) ⁶⁺, Mn_(1/4) ⁴⁺La_(1/4) ³⁺Sb_(1/8) ⁵⁺Ta_(1/8) ⁵⁺Ho_(1/8) ³⁺Yb_(1/8) ³⁺.

In addition, in said doping element or element composition, the mole percentage of doping ions or ion compositions is 0-20%. For instance, in a BT-based electrocaloric ceramics, mole percentage of doped elements or element compositions is 3%.

In addition, said additives can be chosen from one or more than one from MnO₂, MgO, CuO, ZnO, and Sb₂O₅; Proper addition of the additives may reduce the dielectric loss and electric conductivity. The said sintering aids can be chosen from one or more than one from B₂O₃, Li₂O, SiO₂, B₂O₃, and PbO. The purpose of the said sintering aids may reduce the sintering temperature of the ceramics. Glass phase additives can be chosen from one or more than one from B₂O₃, Li₂O, Na₂O, MgO, Al₂O₃, SiO₂, CaO, V₂O₅, Cr₂O₃, Co₂O₃, ZnO, CuO, Sb₂O₅, BaO, and Bi₂O₃. Addition of said glass phase additives not only can reduce sintering temperature, but also effectively reduce porosity of sintered ceramics and thus enhance density and breakdown strength, resulting in an improved electrocaloric performances.

In one embodiment of the present disclosure, a method of utilizing BT-based electrocaloric ceramic, Ba(Zr_(0.2)Ti_(0.8))O₃, to enhance performances of cooling devices based on such electrocaloric ceramics is provided. Said BT-based electrocaloric ceramic, Ba(Zr_(0.2)Ti_(0.8))O₃, is comprising of ceramic, Ba(Zr_(0.2)Ti_(0.8))O₃, and doping elements Mn, Ce; the composition of doping ions is Mn_(0.4) ⁴⁺Ce_(0.6) ⁴⁺; the mole percentage of the doping ion composition is 2% of mole quantity of base ceramics.

In one embodiment of present disclosure, a method of utilizing BT-based electrocaloric ceramic, (Ba_(0.8)Sr_(0.2))(Ti_(0.85)Zr_(0.1)Sn_(0.05))O₃, to enhance performances of cooling devices based on such electrocaloric ceramics is provided. Said BT-based electrocaloric ceramic, (Ba_(0.8)Sr_(0.2))(Ti_(0.85)Zr_(0.1)Sn_(0.05))O₃, is comprising of ceramic, (Ba_(0.8)Sr_(0.2))(Ti_(0.85)Zr_(0.1)Sn_(0.05))O₃, and doping elements Mn, Co, Nb, Sin, Eu, Gd, Tb, Dy, Ho, Er; the composition of doping ions is Mn_(0.1)Co_(0.1)Nb_(0.1)Sm_(0.1)Eu_(0.1)Gd_(0.1)Tb_(0.1)Dy_(0.1)Ho_(0.1)Er_(0.1); the mole percentage of the doping ion composition is 2% of the mole quantity of base ceramics.

FIG. 1 shows the temperature change as a function of electric field for Ba(Ti_(0.8)Zr_(0.2))O₃. FIG. 2 show the temperature change for the doped material, 0.8[Ba(Ti_(0.82)Zr_(0.18))O₃]−0.2[Ba(Ti_(0.9)Sn_(0.1))O₃]. It is clear that Sn-doped BZT showed much better EC response compared with pure BZT.

Only the preferred embodiment of the present invention and examples of its versatility are shown and described in the present disclosure. It is to be understood that the present invention is capable of use in various other combinations and environments and is capable of changes or modifications within the scope of the inventive concept as expressed herein. Thus, for example, those skilled in the art will recognize, or be able to ascertain, using no more than routine experimentation, numerous equivalents to the specific substances, procedures and arrangements described, herein. Such equivalents are considered to be within the scope of this invention, and are covered by the following claims. 

What is claimed is:
 1. A cooling device including an electrocaloric (EC) ceramic as at least one of a refrigerant wherein the EC ceramic possessing a large electrocaloric effect (ECE) and has chemical composition of (Ba_(1-n)Sr_(n))(Ti_(1-x-y)Zr_(x)Sn_(y))O₃ which can be doped; wherein 0.0≦n≦0.6, 0.0≦x≦0.6, 0.0≦y≦0.6; wherein A-site doping element(s) can be chosen from Li, Na, K of IA group, Ca of IIA group, Pb of IVA group, Bi of VA group, Y of IIIB group, La, Ce, Pr, Nd, Pm, Sm of Lanthanide series of elements, and a combinations of thereof; wherein B-site doping element(s) can be chosen from Mg of IIA group, In of IIIA group, Sb of VA group, Cu of IB group, Zn, Cd of JIB group, Sc of IIIB group, Hf of IVB group, V, Nb, Ta of VB group, Cr, W of VIB group, Mn of VIIB group, Fe, Co, Ni, Pd of VIII group, and Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu of Lanthanide series of elements, and the combinations of thereof.
 2. The device of claim 1, wherein 0.0≦n≦0.5, 0.05≦x≦0.4, 0.05≦y≦0.5.
 3. The device of claim 1, wherein the doping elements can be chosen from both ions which have equivalent ionic valence state to ions in the ceramic base and ions which have non-equivalent ionic valence state to ions in the ceramic base.
 4. The device of claim 1, wherein a total mole percentage of doping element or doping elements is 0-20% of the ceramic base.
 5. The device of claim 1, wherein the BT includes an additive selected from one or more of MnO2, MgO, CuO, ZnO, and Sb₂O₅; or a sintering aid selected from one or more of B₂O₃, Li₂O, SiO₂, Bi₂O₃, and PbO; a glass phase filler selected from one or more of B₂O₃, Li₂O, Na₂O, MgO, Al₂O₃, SiO₂, CaO, V₂O₅, Cr₂O₃, Co₂O₃, ZnO, CuO, Sb₂O₅, BaO, and Bi₂O₃. 